1. Field of the Invention
The present invention relates to a method of monitoring a cooling system provided with a refrigerator and a compressor and also relates to a cooling system.
2. Description of the Related Art
Gifford-McMahon (GM) refrigerators, pulse tube refrigerators, Stirling refrigerators, and Solvay refrigerators are capable of cooling a target object to a temperature ranging from a low temperature of about 100 K (Kelvin) to an extremely low temperature of about 4 K. Such refrigerators are used to cool a superconducting magnet, a detector, a cryopump, etc. The refrigerator is provided with a compressor for compressing helium gas used as an operating gas in the refrigerator.
A refrigerator or a compressor needs periodic maintenance. Operators of an apparatus in which a refrigerator is used (e.g., a superconducting magnet system such as a magnetic resonance imaging (MRI) system) typically stop the operation of the refrigerator and the compressor in a well-prepared maintenance plan, considering impact on the MRI system operation.
Meanwhile, the operation of the refrigerator or the compressor may stop suddenly, aside from the planned stop for reasons of maintenance, (hereinafter, referred to as an abnormal stop or failure). In the event of an abnormal stop, liquid helium in the MRI system may evaporate and it may result in disadvantages, such as a quench of the superconducting coil or failure to perform a planned MRI examination.
As one means to overcome damage due to an abnormal stop, there is proposed a technology of predicting a failure of the refrigerator or the compressor.
This technology improves on the reliability of failure prediction techniques based on variation of a single parameter as taught in the related art. Using a single parameter is poor because the parameter may be significantly affected by variation in external variables such as the environment.